A cluster of earthquakes that rattled BC’s coast last week has elicited renewed questions around the geological vulnerability of the region.
Over the past few weeks, there have been at least eight quakes off the northern coast of the province, the majority of which ranged from 5.0 to 6.0 in magnitude.
Despite the buzz around the potential for a damaging quake off the southern coast, SFU professor of earth sciences John Clague says that citizens should not view these rumblings as a precursor to a larger event. “It’s kind of interesting, but it doesn’t present a risk to us,” he assured The Peak.
Vancouverites have been warned over the course of their lives of the possibility of a potentially disastrous earthquake, akin to those that hit the coast of Sumatra in 2004 or Japan in 2011. Similar geological conditions to those regions exist off the coast of Vancouver Island, where the Juan de Fuca Plate is subducting beneath the North American Plate.
Clague explained the risk: “That’s what we call a subduction zone, where one plate is colliding and going down beneath another one, and that’s the kind of environment in which you get earthquakes like the Japanese earthquake a few years ago.”
“It’s kind of interesting, but it doesn’t present a risk to us.”
John Clague, SFU professor of earth sciences
While the earthquakes last week were related to the Queen Charlotte Fault — not the subduction zone that would be the cause of the “Big One” — Clague does find the events of last week scientifically curious.
“What struck me as a little odd was that there was a cluster of [earthquakes],” he remarked. “That was interesting because normally they would occur more spaced in time, and to get a cluster like that, it makes you wonder what’s going on.”
For Brent Ward, SFU professor of earth sciences, the events are common. “We quite often get clusters of these small earthquakes,” he said. “It’s fairly typical, it’s just that there have been a few that have been above 4.0 and above 5.0 [. . .] which is a little bit surprising.”
Both researchers emphasized that a larger event cannot be predicted based on these incidents. Clague explained, “These really big ones, these magnitude 8.0 and 9.0, they’re not preceded by foreshocks, so we don’t get kind of a build up in small earthquakes and then ‘boom,’ the Big One occurs. Typically they seem to occur without warning.”
The last large-scale earthquake on our coast occurred just over 300 years ago, “so we’re getting into the range of when we might expect one,” said Ward. “It could happen tomorrow, it could happen in 300 years. It’s really hard to plan for these low-frequency high-consequence disasters.”
Despite the inability to predict the Big One, Ward stressed the importance of common sense: “It’s always good to have a reminder for people that we are in an earthquake zone, and just to take some basic precautions.”